In parallel type hybrid vehicles, an engine clutch is disposed between an engine and a drive motor. It is thus easy to transfer the power from the engine to wheels. Particularly, when the parallel type hybrid vehicle decelerates, it enters a regenerative braking mode in such a way that the engine stops, and the engine clutch is released to directly absorb the braking energy of the motor.
The term state of charge (SOC) refers to a state of charge of a high-voltage battery, in other words, the amount of charge of the battery. The high-voltage battery functions as a damper to charge or discharge the motor so that the engine can operate at its optimum efficiency.
However, if the engine excessively, frequently alternates between start and stop, the fuel efficiency thereof is reduced, and the load applied to the entire system is increased. Therefore, it is necessary to appropriately control the hybrid system by sufficiently reflecting a driver's intention, whereby the start and stop of the engine can be efficiently and reliably conducted.
Recently, due to the increase in the fuel efficiency of vehicles and the discharge regulations, a demand for environmentally-friendly vehicles has been increasing. Hybrid vehicles are in the spotlight being touted as a realistic solution to those needs.
The above described hybrid vehicles use, as power sources, internal combustion engines and also the motors which use electrical energy. Therefore, control of the SOC of batteries which are storage devices for the electrical energy is significant and important.
Therefore, manufacturers are striving to develop hybrid vehicles which use the optimum driving control strategy to enhance the fuel efficiency in consideration of the SOC. A representative conventional driving control strategy was proposed in Korean Patent Publication No. 10-2013-0024413 A.
Referring to the prior art, the SOC of the battery is sectioned into a plurality of ranges, and a separate power distribution strategy is used in each SOC range. That is, the amount of torque generated from an engine and the amount of torque generated from a motor can be determined based on the power distribution strategy, such as a separate driving map corresponding to each range. It is determined that the current SOC belongs to each SOC range, and driving of the vehicle is controlled under the power distribution strategy corresponding to the determined SOC range.
With regard to the power distribution strategy, in a comparatively low SOC range, the torque generated from the motor is reduced so that the SOC is prevented from being further reduced. The power generated from the engine is used to drive the vehicle and charge the battery, thus increasing the SOC. Furthermore, when the SOC is low, an idle charge is conducted using the engine power. If the SOC is very low, the battery is disconnected from electronic components. In a high SOC range, the SOC is reduced so that the proportion of the torque generated from the motor is increased, thus restraining the use of the engine as much as possible, whereby the fuel efficiency of the vehicle can be enhanced.
Recently, because of rapid improvement of information technology (IT) installed in vehicles, a vehicle can easily obtain various information about a road on which the vehicle is being driven. If this information is reflected in driving strategy for the vehicle, the driving strategy can be improved so that the fuel efficiency of the vehicle can be further enhanced.
The foregoing is intended merely to aid in the understanding of the background of the present disclosure, and is not intended to mean that the present disclosure falls within the purview of the related art that is already known to those skilled in the art.